Mean temperature of winding when current falls

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Homework Help Overview

The discussion revolves around calculating the mean temperature of a winding when the current falls, utilizing resistance and temperature coefficients. The original poster attempts to apply the resistance-temperature relationship but encounters discrepancies in their calculations.

Discussion Character

  • Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between resistance and temperature, questioning the calculations and the sequence of operations used in the equations. There is an attempt to clarify where the original poster may have made errors in their manipulation of the formula.

Discussion Status

Some participants have provided feedback on specific steps in the calculations, suggesting that there may be errors in the order of operations. The original poster expresses confusion about their results, indicating an ongoing exploration of the problem.

Contextual Notes

There is mention of a reference source, B.L. Theraja, which may influence the understanding of the equations being used. The original poster's calculations are based on assumptions that may need further examination.

DevonZA
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Homework Statement


upload_2016-5-1_12-0-27.png


Homework Equations


R2=R1(1+alpha(t2-t1))

The Attempt at a Solution


R1=250/5=50ohms
R2=250/3.91=63.94ohms

R2=R1(1+alpha15degrees(t2-t1))
63.94=50(1+1/254.5(t2-15))
t2=

Now I found this online but the answers provided still don't match, 84.25 being the closest.

upload_2016-5-1_12-12-12.png


When I manipulate the equation I get a totally different answer:
63.94=50(1+1/254.5(t2-15))
63.94/50=(1+1/254.5(t2-15))
1.2788/1+1/254.5=t2-15
1.274=t2-15
t2=1.274+15=16.274 degrees

Please help me understand where I am going wrong.
 
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DevonZA said:
where I am going wrong.
DevonZA said:
63.94/50=(1+1/254.5(t2-15))
1.2788/1+1/254.5=t2-15
upload_2016-5-1_12-12-12-png.100061.png

Is this from B.L. Theraja?
 
Not sure I found it online
 
DevonZA said:
Not sure I found it online
It is from B.L. Theraja. The page looks familiar. The red line in the above post is your error.
 
What have I done wrong though? Every way I enter it into my calculator yields an incorrect answer
 
DevonZA said:
63.94/50=(1+1/254.5(t2-15))
1.2788/1+1/254.5=t2-15[/\QUOTE]
This step is wrong. Check the sequence of operations.
 
Ah I got it :-) thank you
 

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